feat(rust): Implementation of missing RUST feature

[thechandanbhagat]

Summary

This PR implements automatic reconnection support in the Rust SDK, closing the feature gap with the TypeScript SDK's RelayTunnelConnector reconnect loop.

Previously the Rust SDK had no automatic reconnection — callers had to detect disconnection and call connect() manually. This PR adds:

1. connect_persistent() — a new method on RelayTunnelHost that wraps the relay connection in a retry loop with exponential back-off
2. Refactored internal helpers so both connect() and connect_persistent() share the same connection logic

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New API

// Connect once (unchanged behaviour)
let handle = host.connect(&token).await?;

// Connect with automatic reconnection
let opts = ReconnectOptions {
    max_attempts: None,          // retry indefinitely
    initial_delay_ms: 1_000,     // 1 s initial delay
    max_delay_ms: 13_000,        // cap at 13 s (matches TypeScript SDK)
};
let persistent = host.connect_persistent(token, opts).await?;

// Watch connection-state changes
let mut state_rx = persistent.state.clone();
tokio::spawn(async move {
    while state_rx.changed().await.is_ok() {
        println!("State: {:?}", *state_rx.borrow());
    }
});

// Graceful shutdown
persistent.stop().await?;

New types

Type	Description
RelayConnectionState	Connected / Reconnecting { attempt, delay_ms } / Disconnected
ReconnectOptions	Controls backoff: max_attempts, initial_delay_ms, max_delay_ms
PersistentRelayHandle	Returned by connect_persistent() — holds state receiver + stop signal

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Implementation Details

• Fail-fast first connection: the first attempt is made eagerly inside connect_persistent() so callers surface configuration errors immediately (no background goroutine races)
• Exponential backoff: delay doubles on each failed attempt, capped at max_delay_ms (default 13 s, matching TypeScript behaviour)
• Clean shutdown: dropping PersistentRelayHandle (or calling .stop()) signals the reconnect loop to exit gracefully
• Stop signal on backoff sleep: the select! during the sleep also listens for a stop signal so shutdown is responsive even while waiting
• Shared connection logic: connect() now delegates to relay_connect_once(), and connect_persistent() calls it in a loop — no code duplication

Backoff behaviour (mirrors TypeScript RelayTunnelConnector)

attempt 1 → wait 1 s
attempt 2 → wait 2 s
attempt 3 → wait 4 s
attempt 4 → wait 8 s
attempt 5+ → wait 13 s (cap)

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Files Changed

File	Change
rs/src/connections/relay_tunnel_host.rs	Added connect_persistent(), new types, extracted free functions
rs/src/connections/errors.rs	Added MaxReconnectAttemptsExceeded(u32) error variant
README.md	Updated feature matrix: Reconnection ✅ for Rust

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Testing

Rust Analyzer (via VS Code) reports no errors. An OpenSSL system dependency prevents running cargo build locally on Windows without vendored OpenSSL — the logic has been cross-referenced against the equivalent TypeScript implementation in ts/src/connections/relayTunnelConnector.ts.

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Code of Conduct

• I have read and agree to the Code of Conduct

[Copilot]

Pull request overview

Updates the repository’s SDK Feature Matrix documentation to accurately reflect that the Rust SDK supports reconnection (aligning README with the Rust RelayTunnelHost::connect() guidance mentioned in the PR description).

Changes:

• Marked Reconnection as supported (✅) for the Rust SDK in the README feature matrix.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 11 comments.

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